Field
The aspects of the present disclosure relate generally to lighting apparatus, and more particularly, to an optical system for a solid state lighting apparatus.
Description of Related Art
Electronic devices such as a lighting apparatus based on solid state light emitting sources typically require operation at relatively low temperatures for device performance and operational reliability. For example, the junction temperature for a typical light emitting diode (“LED”) device should be below about one-hundred and fifty degrees Celsius (150° C.) or, more preferably, below about one-hundred degrees Celsius (100° C.). At these low operating temperatures, the radiant heat transfer is relatively low, hence conductive and convective heat transfer must be relied upon to properly dissipate heat for maintaining performance. To augment heat transfer, such LED light sources are typically equipped with a thermally-efficient heat sink.
A heat sink is a component providing a large surface area for radiating and convecting heat away from an electronic device. In a typical LED lamp, the heat sink is a relatively large metal component having a large surface area, for example, by the inclusion of thin fins or other heat dissipating structures along the exterior surface of the heat sink. The large mass of the heat sink efficiently conducts heat away from the LED device to the fins, and the large surface area of the fins provides efficient heat dissipation by radiation and convection. As the power requirements for LED lamps increase, the heat transfer requirements become more challenging. Thus, there is a continuous need to devise systems for efficient removal of heat from electronic devices such as high power LED lamps.
To augment heat dissipation, it is known to employ active cooling systems which incorporate fans, heat pipes, or fluid coolants, to provide a flow of cooling fluid or air across the heat sink of an LED lamp. In this way, heat is removed by convective heat transfer. While such active cooling systems are viable for electronic systems which are not space-constrained, difficulties arise when attempting to integrate such systems with a conventional household flood lamp/bulb employing a solid-state LED light source. That is, there are presently no satisfactory active cooling devices which integrate together with supporting subsystems, e.g., conduits, wiring harnesses, actuation mechanisms etc., of a conventional LED lamp.
There is also a need to improve optical efficiency of LED lamps. In this regard, to achieve a desired light intensity distribution, such as omnidirectional light, some existing LED lamps use a diffusing dome that encloses a light engine and a reflector. The reflector is spaced from the light engine and redirects some of the emitted light in one or more desired directions. While such reflectors provide the desired re-distribution of light, reflectors can have the adverse effect of absorbing light energy which increases the heat transfer requirements.
Alternatively, to achieve a desired intensity distribution, some existing lamps surround the emitter with a total internal reflection (“TIR”) lens. Examples of such lenses are disclosed in US Patent Publications US2010/0123397 to Tian et al. and US2011/0170299 to Takase et al. However, such lenses surrounding the emitter are thick and expensive to mold. Further, they often have high light loss and occupy substantial volume in the diffusing dome.
Moreover, the total lumens of light exiting the diffusing dome of such LED lamps is always less than the total lumens of light emitted from the bare LED light engine. This loss of lumens is believed to be due to the absorption and/or diffusion of light by subsystems of the lamp.
Finally, it is difficult to achieve an aesthetically pleasing lamp profile, whether or not the lamp is illuminated or unpowered. In lamps of the prior art, the reflector or lens is frequently visible through the diffusing dome.
A need, therefore, exists for a LED lighting apparatus which distributes light uniformly while being optically efficient, economical, and aesthetically pleasing.